Substrate integrated waveguides are easily manufactured and have a low insertion loss. Also, due to a high quality factor thereof, substrate integrated waveguides have been selected as an electromagnetic wave transmission method appropriate for millimeter wave circuits.
Substrate integrated waveguides are pseudospherical waveguides in which two parallel metallic via holes or via walls are periodically arranged on a general printed circuit board (PCB).
Generally, since substrate integrated waveguides include a vertical axis wall surface formed as a metallic via hole, a surface current does not flow widthwise. Accordingly, substrate integrated waveguides only have a TEm0 mode and a basic electric wave mode is TE10 mode. To reduce sizes of substrate integrated waveguides described above, there are disclosed a half mode substrate integrated waveguide and a folded substrate integrated waveguide. Although a lot of passive elements have been developed based a transmission cable, the development of substrate integrated waveguide-based active elements is imperceptible.
Generally, since two isolated DC conductors exist in each of transmission cables such as a microstrip and a coplanar waveguide (CPW), it is easy to integrate with active elements. However, since substrate integrated waveguides have a short circuit structure in which the entire surface of a substrate is shielded, it is impossible to DC bias. Similarly, in the case of spherical waveguides, to integrate active elements, it is necessary to use a diode mount which is a complicated mechanical structure. However, since it is expensive and complicated, it has a difficulty in being applied to substrate integrated waveguides. Accordingly, there are provided corrugated substrate integrated waveguides. Corrugated substrate integrated waveguides are formed by replacing conductive vias having the form of side electric walls of substrate integrated waveguides with λg/4 microstrip open stubs. This structure has TE10 as a basic mode identical to substrate integrated waveguides. However, since a ground surface and an upper side of a substrate integrated waveguide are perfectly isolated from each other, it is possible to DC bias.
However, in each of corrugated substrate integrated waveguides, since open stubs are arranged in an E-plane direction and a cross-sectional area increases, it is difficult to be coupled with other circuits. Also, corrugated substrate integrated waveguides operate as microstrips of one wavelength, thereby basically generating a leakage mode. Accordingly, generated leakage radiation distorts signals due to coupling with an adjacent circuit and increases radiation loss.
As a cited reference, there is disclosed Korean Patent Registration No. 10-1090857 (registered in Dec. 1, 2011).